The subject matter disclosed herein relates to an uninterruptible power supply (UPS) system, and particularly to methods for detecting the voltage quality of a UPS system.
UPS systems generally convert an alternating current (AC) voltage to direct current (DC) voltage using a rectifier, and from DC voltage to a controllable AC voltage using an inverter. As such, UPS systems offer a significant amount of protection because a load can always be fed using the controllable AC voltage output by the inverter. However, UPS systems may have limited efficiency due to all of the components within the rectifier and the inverter, which can result in a higher operation cost, particularly for large UPS systems. To compensate for the limited efficiency associated with UPS systems, the load connected to a UPS system may be fed via a bypass feed path when a utility power source has a power quality that is within certain tolerance levels. That is, the load may be powered directly from the utility power source when its power quality is determined to be within certain limits. By providing power to the load via the bypass path (i.e., economic mode of operation), the UPS system limits the use of the rectifier and inverter in the inverter feed path of the UPS system.
However, while operating in an economic mode of operation (e.g., ECO mode), the UPS system cannot actively condition the AC voltage provided to the load because the AC voltage is being supplied to the load via the utility power source with little conditioning. As such, some distorted AC voltage signals from the utility power source can be input to the load because the distorted AC voltage signals could still be within the power quality tolerance levels mentioned above. These distorted AC voltage signals input to the load are generally undesirable for the load because they could cause damage to the load, cause the load to operate inefficiently, and so forth. Moreover, various power quality standards impose restrictions on the amount of voltage distortion that can be provided to the load.